In the field of silver halide photographic elements, it is a common practice to incorporate into a layer of the photographic element appropriate dyes absorbing specific wavelengths of light. Said dyes may be used in any layer of the photographic element, such as an interlayer, a radiation sensitive layer, an overcoat layer, an undercoat layer, a backing layer, and may be used for a variety of purposes, such as filter dyes, antihalation dyes, antiirradiation dyes or for the sensitivity control of the photographic emulsion.
The layers of the photographic elements to be added with the dyes are usually made of gelatin or other hydrophilic colloids. The dyes should have an appropriate spectral absorption according to the intended use, should be photographically inert (not affording adverse effects--such as a decrease of sensitivity, fading of the latent image, and fogging--on the performance of the silver halide emulsion layer), should be decolored or dissolved and removed during the photographic processing, and should leave little or no stain in the processed film.
Recently, information recording equipment using semiconductor laser diodes emitting in the infrared region of the electromagnetic spectrum have been developed which require silver halide photographic elements sensitive in the same area. Examples of said equipments are the laser scanners using laser diodes which have a much longer operational life and are less expensive and smaller than conventional gas lasers such as helium-neon or argon lasers. The infrared sensitive silver halide photographic elements for use with laser scanners using laser diodes need dyes for halation prevention and irradiation prevention. These dyes must absorb light in the infrared region. To this purpose, many infrared absorbing dyes have been hitherto proposed. U.S. Pat. No. 4,362,800 discloses indolotricarbocyanine dyes having two sulfoalkyl groups for use in antihalation layers, which, however, leave a greenish stain after processing. To solve the problem of staining, indolotricarbocyanine dyes for use as infrared absorbing dyes have been proposed in U.S. Pat. Nos. 4,839,265; 4,871,656; 4,876,181 and 4,933,269 and in European Patent Application Nos. 342,576 and 342,939.
A problem with these dyes is the inability to have adequate spectral absorption in the infrared region of the electromagnetic spectrum. Usually said dyes have an absorbance maximum in the desired wavelength range in molecular form but aggregate to cause a shift in the maximum absorbance wavelength. Accordingly, a deaggregating compound is usually necessary to enable said dyes to have the desired absorption maximum wavelength. Deaggregants, however, can cause adverse photographic effects, such as speed loss during storage. U.S. Pat. No. 4,871,656 discloses certain indolotricarbocyanine infrared filter dyes which do not require a deaggregant, because said dyes have an absorbance maximum in the desired wavelength range in the molecular form and do not aggregate. Such dyes in order not to have the molecular absorption at wavelengths that are too short are preferably benz[e]indoletricarbocyanine dyes. However, benz[e]indole rings are prepared from dangerous naphthylamine starting compounds. Accordingly, there is still the need to provide infrared absorbing filter dyes having the molecular absorption in the desired wavelength range to be useful as infrared filter dyes, without the shift to the desired wavelength range brought about by aggregation, and which can be synthetized using non-toxic intermediates.
U.S. Pat. No. 4,933,269 describes indolotricarbocyanine infrared absorbing filter dyes, having a 5- or 6-membered heterocyclic ring attached to the methine chain. Examples of heterocyclic rings include piperidine, pyrrolidine, indoline, 3-pyrroline, piperazine, morpholine, thiomorpholine, and other saturated heterocyclic rings. However, it has been noted in the present invention that the filter dyes of U.S. Pat. No. 4,933,269 display radiation in absorption at wavelengths at or beyond 750 nm, when they are benz[e]indolotricarbocyanine dyes and can aggregate.